As electronic technologies are fast developed, hardware and software are both quickly and continuously improved. Nowadays, digital data access devices fall into three main categories: the magnetic disk, the compact disk (CD) and the flash memory. The magnetic disk utilizes magnetic properties of magnetic media for data storage. The magnetic disk further falls into two categories: the fixed hard disk drive (HD) and the portable floppy disk drive. Common magnetic media includes magnetic disks, magnetic tapes . . . etc. They are most commonly used in modern computer systems for data storage.
The compact disk, usually referred to as a small disk, utilizes optical burning for digital data storage. The compact disk has a data storage structure separated into two levels: the session level and the track level. The compact disk is advantageous with its large data capacity and portability today. However, compared to data capacity, reading speed and reusability of the hard disk drive, the compact disk cannot replace the hard disk drive.
The hard disk drive is also not replaced by the floppy disk drive. The floppy disk drive, used for common personal computers, is advantageous with its portability. However, as the demand amount for data exchange grows larger and larger, the small-data-capacity and slow-reading-speed floppy disk drives are gradually eliminated through competition.
With large data capacity and fast reading speed, the hard disk drive is the most popular data access apparatus in current computer systems. The hard disk drive comprises a plurality of magnetic disks on which data are stored magnetically. Each magnetic disk has two surfaces for data storage; each surface of the magnetic disk has a plurality of concentric circular areas called tracks. Each track is separated into a plurality of sectors. A sector is the smallest unit for data access in a disk drive.
The cylinder, head and sector are the three major parts of a hard disk drive. The cylinder is formed by a plurality of tracks at corresponding positions on different disks. The head is corresponded to the number of disk surfaces. The sector is a common unit used for both the hard and floppy disk drives, and is the smallest unit for data access in a disk drive. A sector has a size of 512 bytes.
The above cylinder and head, where the target sector locates, determine the addressing or mapping work for a hard disk drive. This addressing or mapping method is called the CHS (Cylinder Head Sector) mapping or CHS addressing method. However, during the method was developed, the IDE interface, which is used for integrating the hard disk into the personal computer system, could support a single hard disk drive only 512 MB as the maximum capacity.
Later, Large mode, a new working mode for the addressing method, came out and solved the problem. The Large mode enables the hard disk to have a capacity up to 2 GB. Another more popular addressing method for the hard disk drive is the Logical Block Addressing (LBA). LBA is able to support hard disks with capacity more than 8.4 GB.
The logical block addressing method utilizes logical reflection for addressing specific sectors and is broadly used in some of the common interfaces devices in current personal computer systems like enhanced IDE interface devices and small computer system interface (SCSI) devices. Conventional addressing/mapping works for the hard disk drive are physical addressing/mapping. For example, we can track a sector to a detail of on which disk and track the sector is. This kind of description for the sector location also represents the physical location of the sector in a hard disk drive in reality.
Accordingly, the compact disk is easy to carry but it still is not a choice for replacing the conventional hard disk drive (HDD) for the unsolved limitations such as the data capacity and reading speed.
A number of technological challenges affect the HDD industry. One goal is to squeeze more data bits into available storage space. To achieve this goal, the data bits are written inductively by a perpendicular-recording technology, rather than a conventional longitudinal-recording technology. The perpendicular-recording technology may enable smaller bit size and increase storage density. However, those advantages of the perpendicular-recording technology are limited, because the bits of magnetic medium of a data storage medium are arranged in only one plane orthogonal to a read-and-write head.